When a "spine" originates from a stem
modification and arise from the
axillary or apical
bud it is defined
thorn. If
it arises from the
epidermis outside the
branch it is called
prickle, when
it originates in leaves'
margin or
apex it is defined a marginal (or
Apical) tooth.
Nearly all cacti and some
succulents have spines.
In Cactaceae, spines
are a modified leaf lacking
vascular tissue that arise
and multiply from the
areoles and detach easily. They
are classified into central
spines located centrally on the areole and
radial spines around the margins,
they can be stout and woody or fine
and hair-like,
woolly,
bristly,
needle-like,
barbed,
hooked or curved and variously
coloured. Unlike other
flowering plants that are
principally identified by flower and
fruit morphology,
cacti are
identified primarily by their
spine clusters morphology.
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|
Papyraceous spines of
Toumeya papyracantha |
They protect the fat stem against some predators, even if
inefficiently, but their most important function is to condense
atmospheric moisture from dews, fog and rain (spines operate as a
drip tip) so that they drip to
the ground near the base of the
plant for uptake by the superficial
root system.
Often spines protect
plants from the sun and from extreme temperatures, helping to preserve
the plants from drying out.
They also allow to
camouflage the plant
(mimesis).
|
New tender
spring spines in early
growth resumption of
Neoporteria coimasensis |
In succulents the
spines often grow right from the stem
tissue and are called
thorns. |
(Compare with thorns,
prickles,
bristle,
glochid)
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